RNAase protection assay
Sensitive and quantitative alternative to Northern blots for the measurement of gene expression levels. Labelled antisense cRNA is transcribed from a DNA clone in an ...

sauvagine
Peptide (40 amino acids) originally isolated from the skin of the frog, Phyllomedusa sauvagei, and that is closely related to corticotrophin releasing factor and to urotensin ...

saxitoxin
Neurotoxin produced by the " red tide" dinoflagellates, Gonyaulax catenella and G. tamarensis. It binds to the sodium channel, blocking the passage of action potentials. Its ...

scaffold proteins
Proteins that remain when chromosomes are digested with DNAase. Many antigenic species have been identified.

scanning electron microscopy
Technique of electron microscopy in which the specimen is coated with heavy metal, and then scanned by an electron beam. The image is built up on a monitor screen (in the same ...

scanning probe microscopy
Methods for visualizing surfaces at microscopic scale that rely on moving a tiny probe over a surface (usually in an x-y scan), and recording some property of interest (current, ...

scanning transmission electron microscopy
(= STEM)
Method of electron microscopy in which image formation depends upon analysis of the pattern of energies of electrons that pass through the specimen. Has comparable ...

scanning tunnelling microscopy
A form of ultra-high resolution microscopy of a surface in which a very small current is passed through a surface and is detected by a microprobe of atomic dimnensions at its ...

scinderin
Protein (80 kD) of the gelsolin family isolated from vertebrate neural and secretory tissue. Subcortical scinderin is redistributed into patches following stimulation of ...

scintillation counting
Technique for measuring quantity of a radioactive isotope present in a sample. In biology, liquid scintillation counting is mainly used for b emitters such as 14C, 35S and 32P ...

scintillation proximity assay
Assay system in which antibody or receptor molecule is bound to a bead that will emit light when b emission from an isotope occurs in close proximity, ie. from a ...

scirrhous carcinoma
Carcinoma having a hard structure because of excessive production of dense connective tissue.

sclereid
Type of sclerenchyma cell that differs from the fibre cell by not being greatly elongated. Often occurs singly (an idioblast) or in small groups, giving rise to a gritty ...

secretory vesicle
Membrane-bounded vesicle derived from the Golgi apparatus and containing material that is to be released from the cell. The contents may be densely packed, often in an inactive ...

sedimentation
Settling of a component of a mixture under the influence of gravity (natural or artificial) so that the mixture separates into two or more phases or zones.

sedimentation coefficient
The ratio of the velocity of sedimentation of a molecule to the centrifugal force required to produce this sedimentation. It is a constant for a particular species of molecule, ...

segment-polarity gene
A segmentation gene, responsible for specifying anterior-posterior polarity within individual embryonic segments. In Drosophila, there are at least 10 such genes, for example ...

segmentation
Organization of the body into repeating units called segments is a common feature of several phyla, eg. arthropods and annelids, although the segments arise by very different ...

segmentation gene
Genes required for the establishment of segmentation in the embryo. In Drosophila about 20 such genes are required.

segregation of chromosomes
The separation of pairs of homologous chromosomes that occurs at meiosis so that only one chromosome from each pair is present in any single gamete.

selectin
Group of cell adhesion molecules that bid to carbohydrates via a lectin-like domain. The name is derived from select and lectin. They are integral membrane glycoproteins with ...

selector genes
A group of genes that determines which part of a developmental pattern cells will be allocated within a developmental segment.

selenium
Essential trace element that must be provided as a supplement in serum-free culture media for most animal cells.

selenocysteine
An unusual amino acid of proteins, the selenium analogue of cysteine, in which a selenium atom replaces sulphur. Involved in the catalytic mechanism of seleno-enzymes such as ...

self-antigens
(= autoantigen)
The antigens of an individual&’s body have the potential to be self-antigens for the immune system and unless clones of immune cells reactive with self-antigens ...

self-assembly
The property of forming structures from subunits (protomers) without any external source of information about the structure to be formed such as priming structure or template. ...

self-cloning
Any system in which inappropriate cell types or organisms are eliminated because they possess some character that allows them to die or to remove themselves from the system. Thus ...

self-incompatibility
Inability of pollen grains to fertilize flowers of the same plant or its close relatives. Acts as a mechanism to ensure out-breeding within some plant species, eg. in the case of ...

self-replicating
Literally, replication of a system by itself without outside intervention. In practice often taken to refer to systems that replicate without the contribution of any information ...

self-splicing
Self-catalysed removal of group 5 introns, mediated by six paired conserved regions.

sem-5
Cell-signalling gene of Caenorhabditis elegans that encodes a protein (228 residues) with SH2 and SH3 domains and that acts in vulval development and sex myoblast migration. ...

semaphorins
Family of proteins that mediate neuronal guidance by inhibiting nerve growth cone movement. Both transmembrane and secreted proteins are included and many domains of the ...

semiautonomous
Of systems or processes that are not wholly independent of other systems or processes.

semiconservative replication
The system of replication of DNA found in all cells in which each daughter cell receives one old strand of DNA and one strand newly synthesized at the preceding S phase. The ...

semipermeable membrane
A membrane that is selectively permeable to only one (or a few) solutes. The potential developed across a membrane permeable to only one ionic species is given by the Nernst ...

Semliki forest virus
Enveloped virus of the alphavirus group of Togaviridae. First isolated from mosquitoes in the Semliki Forest in Uganda; not known to cause any illness. The synthesis and export ...

Senarmont compensation
In interference microscopy, compensation for the phase difference introduced by the object, measured by introducing a quarter-wavelength plate and rotating the analyser: the ...

sericin
Protein found in silk. Very serine-rich - 30% of the residues are serine.

serine
(= Ser; S: 105 D)
One of the amino acids found in proteins and that can be phosphorylated.

serine protease
One of a group of endoproteases from both animal and bacterial sources that share a common reaction mechanism based on formation of an acyl-enzyme intermediate on a specific ...

serosa
A serous epithelium, having serous glands or cells, as opposed to a mucous membrane.

serotonin
(= 5-hydroxytryptamine; 5-HT)
A neurotransmitter and hormone(176 D), found in vertebrates, invertebrates and plants.

serotype
The genotype of a unicellular organism as defined by antisera against antigenic determinants expressed on the surface.

serous gland
An exocrine gland that produces a watery, protein-rich secretion, as opposed to a carbohydrate-rich mucous secretion.

serpentine receptors
(= seven-spanners; seven transmembrane receptors)
Receptors in which there are seven transmembrane-spanning regions. All are G-protein coupled. A variety of names have been used ...

shadowing
Procedure much used in electron microscopy, in which a thin layer of material, usually heavy metal or carbon, is deposited onto a surface from one side, in such a way as to cast ...

shaker
Drosophila gene encoding a potassium channel. Related genes, shab, shal and shaw are known in flies and humans. The mutation is so-called because the fly&’s legs shake under ...

shc
Gene family identified by presence of SH2 domains. Shc also has a tyrosine motif that, when phosphorylated, will bind the SH2 of the adaptor protein grb2 and may link ...

shear stress response element
(= SSRE)
Various cells can be stimulated to divide if subject to fluid shear stress. This is particularly interesting in the case of endothelial and vascular smooth muscle ...

shibire
Drosophila gene that encodes dynamin. Shibire is temperature sensitive and in affected flies synaptic vesicles are depleted at high temperatures but are restored in nerve ...

signal recognition particle
A complex between a 7S RNA and six proteins. SRP binds to the nascent polypeptide chain of eukaryotic proteins with a signal sequence and halts further translation until the ...

signal recognition particle-receptor
Receptor for the signal recognition particle (SRP) found in the membrane of the endoplasmic reticulum. Also known as docking protein. Heterodimeric, both protomers having ...

signal sequence
A peptide present on proteins that are destined either to be secreted or to be membrane components. It is usually at the N-terminus and normally absent from the mature protein. ...

signal transduction
The cascade of processes by which an extracellular signal (typically a hormone or neurotransmitter) interacts with a receptor at the cell surface, causing a change in the level ...

single-stranded conformational polymorphism
(= SSCP)
Technique for detecting point mutations in genes by amplifying a region of genomic DNA (using asymmetric PCR) and running the resulting product on a high quality gel. ...

singlet oxygen
(= (1) O2)
An energised but uncharged form of oxygen that is produced in the metabolic burst of leucocytes and that can be toxic to cells.

sis
An oncogene, identified in monkey sarcoma, encoding a B-chain of PDGF.

site-specific mutagenesis
An in vitrotechnique in which an alteration is made at a specific site in a DNA molecule, which is then reintroduced into a cell. Various techniques are used; for the cell ...

site-specific recombination
A type of recombination that occurs between two specific short DNA sequences present in the same or in different molecules. An example is the integration and excision of lambda ...

situs inversus
Condition in which the normal asymmetry of the body (in respect of circulatory system and intestinal coiling) is reversed. Interesting because it occurs in approximately 50% of ...

SIV
(= simian immunodeficiency virus)
Very similar to HIV and used extensively as an animal model.

Sjogren&’s syndrome
One of the so-called connective tissue diseases that also include rheumatoid arthritis, systemic lupus erythematosus and rheumatic fever. Characterized by inflammation of ...

skeletal muscle
A rather nonspecific term usually applied to the striated muscle of vertebrates that is under voluntary control. The muscle fibres are syncytial and contain myofibrils, tandem ...

sliding filament model
Generally accepted model for the way in which contraction occurs in the sarcomere of striated muscle, by the sliding of the thick filaments relative to the thin filaments. ...

slime moulds
Two distinct groups of fungi, the cellular slime moulds or Acrasidae that include Dictyostelium, and the acellular slime moulds or Myxomycetes that include Physarum.

slot blot
A dot blot in which samples are placed on a membrane through a series of rectangular slots in a template. This is slightly advantageous because hybridization artefacts are ...

slow muscle
Striated muscle used for long-term activity (eg. postural support). Depend therefore on oxidative metabolism and have many mitochondria and abundant myoglobin.

slow reacting substance of anaphylaxis
(= SRS-A)
Potent bronchoconstrictor and inflammatory agent released by mast cells; an important mediator of allergic bronchial asthma. A mixture of three leukotrienes (LTC4 ...

slow virus
(1) Specifically one of the Lentivirinae.
(2) Any virus causing a disease that has a very slow onset. Diseases such as sub-acute spongiform encephalopathy, Aleutian disease of ...

SLS collagen
(= segment long spacing collagen)
Abnormal packing pattern of collagen molecules formed if ATP is added to acidic collagen solutions, in which lateral aggregates of molecules ...

small acid-soluble spore proteins
(= SASP)
DNA-binding proteins in the spores of some bacteria, thought to stabilize the DNA in the A-DNA configuration, so protecting it from cleavage by enzymes or UV light.

small cell carcinoma
Common malignant neoplasm of bronchus. Cells of the tumour have endocrine-like characteristics and may secrete one or more of a wide range of hormones, especially regulatory ...

small nuclear RNA
(= snRNA)
Abundant class of RNA found in the nucleus of eukaryotes, usually including those RNAs with sedimentation coefficients of 7s or less. They are about 100-300 ...

smooth endoplasmic reticulum
An internal membrane structure of the eukaryotic cell. Biochemically similar to the rough endoplasmic reticulum (RER), but lacks the ribosome-binding function. Tends to be ...

smooth microsome
Fraction produced by ultracentrifugation of a cellular homogenate. It consists of membrane vesicles derived largely from the smooth endoplasmic reticulum.

smooth muscle
Muscle tissue in vertebrates made up from long tapering cells that may be anything from 20-500 m m long. Smooth muscle is generally involuntary, and differs from striated ...